With the use of crosslinked epoxy and polyurethane paint systems containing heavy metals and paint primers containing chromates, there has arisen a need for a stripping agent which effectively removes these coatings without attacking the substrate base. Although paint strippers comprised mainly of strong acids have proven capable of removing such paints, their propensity for corrosion of metal substrates has limited their use. Alkaline activated paint removers, based on ammonia, amines and caustic agents have been proposed but have been found to be ineffective in such applications. The most active paint strippers to date are methylene chloride based compositions, however, such highly volatile halocarbons are environmentally objectionable and are suspected carcinogens. Although methylene chloride is fast acting, its effectiveness is short lived due to its volatility; thus, repeated applications of the stripper are required for the removal of all but very thin coated layers. To overcome the problem of volatility, N-alkyl pyrrolidones have been substituted in whole or in part for methylene chloride, however, such compositions are equally objectionable because of the lactam's hydrogen bonding properties in the presence of water leading a significant lowering of the stripping rate.
U.S. Pat. No. 3,355,385 proposes the use of ketones such as acetone and methyl ethyl ketone in formulations with peroxide to provide adequate stripping, but, like methylene chloride, these stripping agents have a short effective life since the ketone component is volatile and extremely flammable.
Other formulations have also failed to meet all of the requirements for stripping compositions such as a high stripping capability, non-flammability, biodegradability and/or freedom from carcinogenic or non-biodegradable chemicals. Accordingly, applicant's aim is to overcome the above difficulties and to provide an ecologically safe, water soluble, biodegradable stripping agent which is resistant to oxidation under ambient conditions and which is non-combustible
It is another object of this invention to provide an ecologically safe stripping composition which effectively removes epoxy and polyurethane containing resinous coatings from a substrate and which minimizes environmental and personal hazards.
Another object is to provide a stripping composition which is non-corrosive to metal surfaces.
Still another object is to provide a process for using the present composition in the removal of resinous coatings without significant damage to aluminum or other metal surfaces.
These and other objects of the invention will become apparent from the following description and disclosure.